The mission of the NCI/CCR/LP Clinical Cytogenetics Section is to provide state-of-the-art diagnostic services for patients evaluated and treated at the Mark O. Hatfield Clinical Research Center; to participate in collaborative clinical translational research; and to teach and mentor students, residents, and fellows in the principles and practices of clinical cytogenetics service and research. The goals of this project, which comprises 85 percent of the effort of the section, are to provide diagnostic service and research testing on samples from patients entered on clinical research protocols by NCI and other Institute physicians, to collaborate on clinical translational research protocols, and to teach and mentor students, residents, and fellows. The Clinical Cytogenetics Section is the only intramural NIH laboratory performing cytogenetics diagnostic services. The laboratory is inspected and certified by the College of American Pathologists, the Joint Commission for Accreditation of Healthcare Organizations, and the Clinical Laboratory Improvement Act of 1988. We currently perform highly complex routine and molecular cytogenetic testing on patient samples from a number of institutes (NCI, NIAID, NHLBI, NHGRI, NIAMS, NIDDK, and NICHD) and the Clinical Center Department of Laboratory Medicine. In 99 percent of cases the testing is for acquired chromosome abnormalities in premalignant and malignant disorders, and in the remaining 1 percent of cases is for constitutional chromosome abnormalities. The results of our testing are used for diagnosis, classification, prognosis, and treatment planning for patients. They also provide critical information regarding the gene regions that may be important for tumor initiation and progression, and thus serve as a starting point for further molecular biologic investigations of malignant diseases. Section members are conducting routine diagnostic and research fluorescence analyses of patients entered on NCI and NHLBI clinical research protocols. Dr. Arthur is an Associate Investigator on 11 NCI and three NHLBI active protocols. The cytogenetics data generated as part of these studies are clinically useful for diagnosis, classification, and treatment assignment for patients. They are also important for monitoring patient response to experimental therapy, and for correlation with other research studies. They have the potential for discovery of new clinical-pathological associations among these diseases and of biological mechanisms that may be targeted with future therapies. Finally, section members teach and mentor students, residents, and fellows in the principles and practices of clinical cytogenetics service and research. In addition to mentoring four summer students and two postdoctoral fellows, Dr. Arthur is a member of the NCI/CCR/LP Resident and NCI/CCR/LP Hematopathology Fellow faculties. In this role, she provides didactic lectures and laboratory rotations for all residents and fellows enrolled in these training programs. In summary, the Clinical Cancer Cytogenetics program provides unique state-of-the-art clinical cytogenetics service, essential education and service to the LP and the CCR, and wide collaborative support for NCI clinical and translational research programs.